Grids

Grid files are important for shifting and transforming between datums

US, Canadian, French and New Zealand

Switzerland

Background in ticket #145

We basically have two shift grids available. An official here:

Swiss CHENyx06 dataset in NTv2 format

And a derived in a temporary location which is probably going to disappear soon.

Main problem seems to be there’s no mention of distributivity of the grid from the official website. It just tells: “you can use freely”. The “contact” link is also broken, but maybe someone could make a phone call to ask for rephrasing that.

HARN

With the support of i-cubed, Frank Warmerdam has written tools to translate the HPGN grids from NOAA/NGS from .los/.las format into NTv2 format for convenient use with PROJ.4. This project included implementing a .los/.las reader for GDAL, and an NTv2 reader/writer. Also, a script to do the bulk translation was implemented in https://github.com/OSGeo/gdal/tree/trunk/gdal/swig/python/samples/loslas2ntv2.py. The command to do the translation was:

loslas2ntv2.py -auto *hpgn.los

As GDAL uses NAD83/WGS84 as a pivot datum, the sense of the HPGN datum shift offsets were negated to map from HPGN to NAD83 instead of the other way. The files can be used with PROJ.4 like this:

cs2cs +proj=latlong +datum=NAD83
      +to +proj=latlong +nadgrids=./azhpgn.gsb +ellps=GRS80
# input:
-112 34
# output:
111d59'59.996"W 34d0'0.006"N -0.000

This was confirmed against the NGS HPGN calculator.

The grids are available at http://download.osgeo.org/proj/hpgn_ntv2.zip

See also

HTPD describes similar grid shifting

HTDP

HTPD describes the situation with HTDP grids based on NOAA/NGS HTDP Model.

Hungary

Hungarian grid ETRS89 - HD72/EOV (epsg:23700), both horizontal and elevation grids

Non-Free Grids

Not all grid shift files have licensing that allows them to be freely distributed, but can be obtained by users through free and legal methods.

Canada NTv2.0

Although NTv1 grid shifts are provided freely with PROJ.4, the higher-quality NTv2.0 file needs to be downloaded from Natural Resources Canada. More info: http://www.geod.nrcan.gc.ca/tools-outils/ntv2_e.php.

Procedure:

  1. Visit the NTv2, and register/login

  2. Follow the Download NTv2 link near the bottom of the page.

  3. Unzip ntv2_100325.zip (or similar), and move the grid shift file NTV2_0.GSB to the proj directory (be sure to change the name to lowercase for consistency) * e.g.: mv NTV2_0.GSB /usr/local/share/proj/ntv2_0.gsb

  4. Test it using:
    cs2cs +proj=latlong +ellps=clrk66 +nadgrids=@ntv2_0.gsb +to +proj=latlong +ellps=GRS80 +datum=NAD83
    -111 50
    
    111d0'3.006"W   50d0'0.103"N 0.000  # correct answer
    

Canada

Canadian NTv2 grid shift binary for NAD27 <=> NAD83.

Austria

Austrian Grid for MGI

Spain

Spanish grids for ED50.

Portugal

Portuguese grids for ED50, Lisbon 1890, Lisbon 1937 and Datum 73

Brazil

Brazilian grids for datums Corrego Alegre 1961, Corrego Alegre 1970-72, SAD69 and SAD69(96)

South Africa

South African grid (Cape to Hartebeesthoek94 or WGS84)

Netherlands

Dutch grid (Registration required before download)